Stacked imager package

ABSTRACT

An imaging system for use in a digital camera or cell phone utilizes one chip for logic and one chip for image processing. The chips are interconnected using around-the-edge or through via conductors extending from bond pads on the active surface of the imaging chip to backside metallurgy on the imaging chip. The backside metallurgy of the imaging chip is connected to metallurgy on the active surface of the logic chip using an array of solder bumps in BGA fashion. The interconnection arrangement provides a CSP which matches the space constraints of a cell phone, for example. The arrangement also utilizes minimal wire lengths for reduced noise. Connection of the CSP to a carrier package may be either by conductive through vias or wire bonding. The CSP is such that the imaging chip may readily be mounted across an aperture in the wall of a cell phone, for example, so as to expose the light sensitive pixels on the active surface of said imaging chip to light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to small imaging packages and, moreparticularly, to the packaging of the semiconductor chips employed inthe imaging systems of small imaging packages.

2. Background and Related Art

Imaging systems for hand held small equipment, such as, cell phones forexample, typically employ image sensing materials in a CMOS chiparrangement. In such arrangements, the CMOS image sensor creates apicture by detecting signals from photodiodes and MOS transistors formedwithin unit pixels integrated into an array on a semiconductor chiparrangement.

In this regard, CMOS image sensor chip arrangements have allowed for theintegration of logic and an imaging array on the same chip. This hasbeen found beneficial in reducing the number of support chips needed inan imaging system, such as, a digital camera or a cell phone. Packagingrequirements often make it difficult to place and wire multiple chipsincreasing the desire to have a total imaging solution on one chip.

However, recent development efforts have caused the amount of logicrequired to be placed on the same chip as the image sensor tosignificantly increase. For example, the amount of logic may now includelogic circuits to implement image processing, such as, color correction,white balance, random and fixed pattern noise suppression, imagecompression, and camera functions, such as, lens motor controls for autofocus and zoom function, among other functions.

The fundamental process for creating a CMOS imaging array is compatiblewith digital logic, but not optimized for such. To create a high qualityimaging array, the process needs to be optimized for low leakage. Thistypically means lengthy high temperature anneals and low doping levelsin the diffusion processes. These processes tend to work against highperformance, high density, logic. Thus, either the density andperformance of the logic suffer, or the process has to be made much morecomplex, doubling the number of implants needed to make separate wells,and diffusions for the logic and for the imaging circuits.

There is also the problem of noise. High performance logic often createsnoise both in the substrate and on the metal levels. This noise candegrade the image quality. Thus, there are a variety of reasons forusing separate chips, one for imaging and one for logic.

Image display systems which have separate chips, one chip for logic andanother chip for imaging, are known. For example, U.S. PatentPublication 2004/0095495 A1 describes one such arrangement. When using atwo-chip approach to implementing imaging systems, various alternativesare available for allocating functions between the two chips. However,independent of how the functions are allocated between the chips, thearrangement and interconnection of the two chips in a small, ruggedpackage within tight space constraints is critical. Moreover, althoughhigh performance logic chips continue to become smaller even with morefunctionality, the imaging chip with imaging array cannot be similarlyreduced without loss of imaging capability. Thus, typically, the logicchip will be interconnected with a larger imaging chip. The ability toeffectively interconnect the two chips to one another to in a chip scalepackage (CSP) and to interconnect the CSP to the carrier package inwhich the CSP is arranged, is an important consideration in fabricating,for example, a cell phone camera module in a cell phone package.

SUMMARY OF THE PRESENT INVENTION

It is, therefore, an object of the present invention to provide animproved imaging system packaging arrangement.

It is a further object of the present invention to provide a packagingarrangement for a two chip imaging system.

It is yet a further object of the present invention to provide aninterconnection method and arrangement for interconnecting a pair ofchips to one another and to the carrier package in which they operate.

It is another object of the present invention to provide an imagingsystem with interconnection arrangements between an imaging chip and alogic chip to form a CSP and between these chips in a CSP and thecarrier package in which the CSP functions.

It is yet another object of the present invention to provide a packagingand interconnection arrangement for an imaging system employing a logicchip and imaging chip for use in a camera module for a cellular phone orthe like.

It is still yet another object of the present invention to provide a CSParrangement for an imaging system employing an imaging chip and a logicchip interconnected using around-the-edge or conductive vias connectedto backside metallurgy and ball grid array (BGA) chip interconnections.

In accordance with the present invention, an imaging system, employed ina cell phone or digital camera, for example, utilizes one chip for logicand one chip for imaging. The logic chip is typically smaller than theimaging chip and is interconnected to the imaging chip through backsidemetallurgy on the imaging chip backside. Imaging chip active surfaceinterconnection to the backside metallurgy is implemented two ways. Oneemploys around-the-edge connections to bond pads on the active surfaceof the imaging chip. The other employs through vias to bond pads on theactive surface. The chip interconnections are such as to create a CSPcomprising an imaging chip and a logic chip.

Interconnection of the CSP to the carrier package may be implementedseveral ways. Where the logic chip acts as the mounting point for theCSP, an array of solder bumps on the backside of the logic chip acts tointerconnect to the carrier package. This array of solder bumps iscoupled by through vias to the active surface of the logic chip. Thisacts to minimize interconnect distance.

Where the imaging chip acts as the mounting point for the CSP, wirebonding is used to connect the CSP to the carrier package. This approachis used for both the around-the-edge and through vias wiring to the backside metallurgy. By mounting the imaging chip to the carrier package,such as, a cell phone housing wall, optical elements required for theimaging chip may readily be positioned and mounted in the aperture.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic view of a typical prior art imaging system.

FIGS. 2A and 2B show a typical prior art imaging system employing animaging chip and a logic chip.

FIG. 3 shows a cross-section of one interconnection and packagingarrangement, in accordance with the present invention.

FIG. 4 shows a backside view of the imaging chip using around-the-edgewiring to an array of solder bumps.

FIG. 5 shows a cross-section of another interconnection and packagingarrangement, in accordance with the present invention.

FIG. 6 shows a cross-section of a further interconnection and packagingarrangement, in accordance with the present invention.

FIG. 7 shows a cross-section of yet another interconnection andpackaging arrangement, in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a typical prior art imaging system employingan imaging chip and processing logic chip. In this particular example,imaging chip 1 includes image sensor 3 for converting light into anelectric signal, horizontal and vertical scanning circuits 5 and 7 fordriving sensor 3, and an amplifier 9 for amplifying the signals ofsensor 3. Also included on imaging chip 1 is a timing pulse inputterminal 11 and an image signal output terminal 13.

Imaging chip 1 is stacked on imaging processing chip 15. Imageprocessing chip 15, in this example, includes timing generator 17, gaincontrol amplifier (GCA) 19, analog/digital converter (ADC) 21 andimaging processing circuit 23. It is clear that in a two chip imagingsystem, some of the various functions required to operate can bearranged on either chip.

However, the logical processes required to operate the variousfunctions, such as, image processing, should be placed on the logicchip. By so doing, the logic processes can be optimized separately fromthe imaging processes, thereby preserving both high quality images andhigh speed, high density logic which is noise isolated from the imagingarray. Image processing may include, among other operations, colorcorrection, white balance, random and fixed pattern noise suppressionand image compression. Digital camera equipment may also include camerafunctions, such as, lens motor control for auto focus and zoom control.

Thus, the description of prior art image processing chip 15 of FIG. 1does not include functions, such as, lens motor control and zoomcontrol, or image processing, such as color connection, white balance,noise suppression and image compression. Where such functions areemployed, they would all be included on the logic chip. In addition,there may be a variety of other features for camera applications thatwould also be included in the logic chip.

FIG. 2A shows one typical arrangement for interconnecting an imagingchip, an image processing or logic chip, and a carrier, stacked in thatorder. As shown, the interconnections are made using wire bonding. FIG.2B shows the same stacking arrangement with the interconnections madeusing conductive through vias. As shown in FIG. 2A, wire bondingoperates from one level to successive lower levels, each larger infootprint. As shown in FIG. 2B, the interconnecting through vias arepositioned around the edge of the chips. In each of FIGS. 2A and 2B, thefootprint of the image processing logic chip is larger than the imagingchip.

FIG. 3 shows, in accordance with the present invention, aninterconnection and packaging arrangement using around edge wiring as,known in the art, and backside metallurgy for the imaging chip. Typicalof such wiring and metallurgy is that described in U.S. Pat. No.6,646,289 assigned to Shellcase Ltd. Such wiring arrangements are knownfor their compactness, mechanical integrity and environmentallyprotected packaging features.

Imaging chip 27 in FIG. 3 includes sensor layer 29. Sensor layer 29typically comprises a pixel array of sensing elements 30 for convertinglight into electric signals. Imaging chip 27 is interconnected withlogic chip 31 using around-the-edge connection metallurgy 33 connectedto bond pads 36 on the active surface of the imaging chip and backsidemetallurgy 35 on the backside of the imaging chip. Insulating material28 may separate the metallurgy from the active surface, as shown.Although not shown, insulating material may also be used to separate allof around-the-edge metallurgy from chip 27. Backside metallurgy 35brings the signals from the imaging chip to solder bumps 37 of a solderbump array or BGA on logic chip 31.

FIG. 4 shows the backside 42 of imaging chip 27 in a typical backsidepattern of metallurgy 35 connected to solder bumps 37. Around-the-edgemetallurgy 33 on sloped surface 40 connects to bond pads (not shown) onthe opposing (active) surface and to backside metallurgy 35 on backside42. As shown, in FIGS. 3, 4 and 5, the around-the-edge metallurgy 33 isconformal to the chip edge, as is backside metallurgy 35 conformal tothe backside of the chip.

Solder bumps 37 in FIG. 3 connect to solder bumps 39 on the backside oflogic chip 31 by way of conductive through vias 41, two of which areshown. Solder bumps 39, in turn, connect to pads 43 on carrier package45. Carrier package 45 may be a substrate, such as, a ceramic substratewhich is mounted to the wall of a device package, such as, a cell phoneor camera. Carrier package 45 may also be attached to other layers ofmaterial. Alternatively, the carrier package may be the wall of a cellphone itself, for example, with logic chip 31 then being attached to thewall with an adhesive.

It is understood that the cross-section of FIG. 3 shows two through viasand their location only by way of example. It is clear that there areothers. These are shown to demonstrate that some signals from imagingchip 27 carry through to BGA's 39 on carrier package 45. Other signalsto BGA's 39 come by way of vias from logic chip 31. The signals going tothe carrier package may be for any of a variety of reasons, such as,various control functions, display, etc.

FIG. 5 shows a cross-section of another interconnection and packagingarrangement, in accordance with the present invention. In thisarrangement, imaging chip 27 is attached to carrier package 47 having anopening or aperture 49 for receiving light. The chip is mounted so as tobridge aperture 49 in a manner that allows sensing layer 29 to beexposed to receive light. As understood by those skilled in the art,imaging chip 27 may be attached to by any of a variety of ways. Forexample, imaging chip 27 may be attached to carrier 47 by an insulatingadhesive or bonding material. Again, carrier package 47 may be the wallof a cell phone or camera, for example. It is clear that in each of thearrangements shown in FIGS. 3, 5, 6 and 7, that various optical lens,filters and transparent coating arrangements may be used for handlinglight incident sensor layer 29 and for protecting sensor layer 29.

By attaching the imaging chip/logic chip CSP so as to bridge theaperture 49, the optical system required may readily be positioned inthe aperture adjacent sensor layer 29 without the physical constraintsof wiring. The around-the-edge conductors, backside metallurgy and BGA'sused as interconnections facilitate such an arrangement in a CSP.

Thus, it can be seen in FIG. 5, that imaging chip 27 is interconnectedto logic chip 31 in the same around-the-edge manner, as described withreference to FIG. 3. Thus, around-the-edge metallurgy 33 and backsidemetallurgy 35 connect to solder bumps 37 which, in turn, are bonded topads (not shown) on the active surface of logic chip 31. However, withchip 27 of the CSP bridging aperture 49, electrical interconnection tothe carrier package in this arrangement is made through wire bonding.Thus, wires 51 are bonded at one end to pads 53 on imaging chip 27 andat the other end to pads 55 on carrier package 47. It can be seen thatpads 53 are shown extending beyond backside metallurgy 35. This is doneto represent the fact that some wires will be connected directly to padson backside metallurgy 35 for receiving signals from imaging chip 27while other wires will be connected to pads that are separate from thebackside metallurgy and are arranged to receive signals from logic chip31. Thus, the latter set of pads connect to backside metallurgy thatconnects to BGAs 37 to receive signals from logic chip 31. One sucharrangement, by way of example, is shown by pad 53 in FIG. 4.

FIG. 6 shows another interconnection and packaging arrangement, inaccordance with the present invention. As in the arrangement of FIG. 5,imaging chip 27 is mounted on carrier package 47 where carrier package47 may be a substrate for chip 27 attached to the housing or walls of acell phone or camera, for example. Alternatively, carrier package 47 maybe the housing or wall, itself, of a cell phone or camera.

In the arrangement of FIG. 6, however, the interconnection betweenimaging chip 27 and logic chip 31 is made using backside metallurgy 36connected by through via connectors 57 to bond pads 59 on the activesurface of imaging chip 27. As shown, the backside metallurgy isconnected to logic chip 31 by solder bumps 37. As in FIG. 5, wire bondconnectors are used to connect the CSP to carrier package 47. Thus, wireconnectors 51 connect pads 55 on carrier package 47 to pads 61 onimaging chip 27. Some pads 61 connect to imaging chip 27 and someconnect to logic chip 31.

FIG. 7 shows an interconnection and packaging arrangement where logicchip 32 has a larger footprint than imaging chip 28. Backside metallurgy38 connects pads 60 on the active surface of imaging chip 28 by way ofthrough vias 58, to solder bumps 40. Solder bumps 40, in turn, connectthe backside metallurgy 38 to pads (not shown) on logic chip 32. Thebackside of logic chip 32 is mounted on carrier package 46. Logic chip32 interconnects to carrier package 46 through wires 52 which are bondedto pads 54 on logic chip 32 and pads 56 on carrier package 46. Althoughnot shown, some of pads 54 connect to imaging chip 28 and others connectto logic chip 32.

It should be understood that in addition to providing a CSP, thearound-the-edge or through via conductors, backside metallurgy and BGAarrangements used to interconnect the two chips, also act to providelimited wire-length interconnections. As such, these limited wirelengths reduce the amount of noise that may be generated. This reductionof noise is in addition to that obtained by virtue of separating thelogic functions from the imaging functions by using separate chips.

It will be understood from the foregoing description that variousmodifications and changes may be made in the preferred embodiment of thepresent invention without departing from its true spirit. It is intendedthat this description is for purposes of illustration only and shouldnot be construed in a limiting sense. The scope of this invention shouldbe limited only by the language of the following claims.

1. A chip package, comprising: a first chip having backside metallurgyand pads on an active surface thereof positioned around the peripheralregion of said active surface, said backside metallurgy connected tosaid pads by through via conductors extending through said first chipfrom said backside metallurgy to said pads; and a second chip havingmetallurgy on an active surface thereof connected to the said backsidemetallurgy of said first chip by an array of interchip solder bumps. 2.A chip package, comprising: an imaging chip having backside metallurgyand pads on an active surface thereof positioned around the peripheralregion of said active surface, said backside metallurgy connected tosaid pads by conductors extending from said backside metallurgy to saidpads; and a logic chip having metallurgy on an active surface thereofconnected to the said backside metallurgy of said imaging chip by anarray of interchip solder bumps.
 3. The chip package as set forth inclaim 2 wherein the said active surface of said imaging chip includesthereon an array of light sensitive pixels located within the positionof said pads around said peripheral region with said pixels arranged togenerate voltage as a function of light.
 4. The chip package as setforth in claim 3 wherein the said imaging chip is mounted across anaperture in the wall of a carrier package so as to expose said array oflight sensitive pixels to light through said aperture.
 5. The chippackage as set forth in claim 4 wherein said imaging chip and said logicchip are electrically connected to said carrier package by wire bonding.6. The chip package as set forth in claim 5 wherein said conductors arearound-the-edge conductors extending conformally around the edge of saidimaging chip to said pads.
 7. The chip package as set forth in claim 5wherein said conductors are through via conductors extending throughsaid imaging chip to said pads.
 8. The chip package as set forth inclaim 3 wherein the backside of said logic chip is mounted on a carrierpackage.
 9. The chip package as set forth in claim 8 wherein said logicchip is electrically connected to said carrier package by wire bonded atone end to pads on said logic chip and the other end to pads on saidcarrier package.
 10. The chip package as set forth in claim 8 whereinsaid logic chip is electrically connected to said carrier package by anarray of solder bumps with some of said solder bumps of said array ofsolder bumps connected by through vias to selected ones of saidinterchip solder bumps.
 11. The chip package as set forth in claim 3wherein the planar area of said logic chip is smaller than the planararea of said imaging chip.